Coarse and fine frequency synchronizing system



Feb. 13, 1945- A. McL.. NICOLSON 2,369,153

COARSE AND FINE FREQUENCY SYNCHRONIZING SYSTEM Original Filed April 12, 1940 2 Sheets-Sheet l mvp use/4447M \l F l 6.3.

. 7 31 f; j 65 e9 imam? J INVENTOR.

A; TOHNEYLS 1945- A. MCL. NICOLSON ,369,

COARSE AND' FINE FREQUENCY SYie'CHRONIZING SYSTEM Original Filed April 12, 1940 2 Sheets-Sheet 2 All I TTORNEYJ Patented Feb. 13, 1945 COARSE AND FINE FREQUENCY SYN- CHRONIZIN G SYSTEM Alexander McLean Nicolson, New York, N. Y.,

assignor to Communication Patents, Inc., a corporation of Delaware Original application April 12, 1940, Serial No. 329,324. Divided and this application November 21, 1941, Serial No. 419,886

1 6 A Claims.

This invention relates to a system for synchronizing by coarse and line frequencies the operation of a plurality of devices situated at spaced apart locations and more particularly relates to systems for synchronizing the operation of television and facsimile transmitters and receivers. This is a division of mycopending application Serial N 0. 329,324, filed April 12, 1946. now Patent No. 2,263,641, dated November 25, 1941, which is a division of my application Serial No. 275,672, filed May 2'7, 1928, now Patent No. 2,197,005, dated April 16, 1940.

In order for a television system to be capable of wide and eliective use, the apparatus should require no greater intelligence and skill on the part of the operator than can be exercised by the average person, as clearly itis impractical to require a highly skilled operator at every station, as for instance at every receiver in a television broa-dcasting system.

The operation of a receiver controlled in speed by a distant transmitter presents two principal difliculties. First, there is the difficulty of maintaining exactly the same speed at both stations, and secondly, there is the difiiculty of bringing the scanning apparatus mechanically in step at both stations as Well. This latter difiiculty may result in parts of the received image being displaced with respect to the other parts. For example, if the scanning apparatus is operating at exactly the same speed at the transmitting station and at the receiving station, and if the receiving scanner'is half way across the screen at the instant the transmitting scanner is operating on the beginning of the image, it will be apparent that at the receiver, the image will be cut in half and the two halves transposed in position.

It is clear that since there is only one space position of the receiving scanning apparatus relative to thetransmitting scanning apparatus which will be correct, when synchrony is established, and there are many possible positions which will be incorrect, some means should be provided which will not only cause the receiving apparatus to come to synchronous speed, but which. will also cause the receiving scanning apparatus to run faster or slower than the transmitting scanning apparatus, until it occupies the same position relatively to the image, and when this identity of relative position is attained, synchronous speedis to be maintained; and furthermore, should the receiver and transmitter get out of step, they must be broughtback in step, and the receiver again brought to synchronous speed.

The images at transmitter and receiver may be considered as fixed within what I term a frame of reference, and each comprises a large number of picture elements scanned in a unit of time and in a predetermined pattern or sequence, each frame being repeatedly scanned at the rate of 16 to 18 frames'per second. If the scanner at the receiver and transmitter are operating at the same speed and pass corresponding points in the frame of reference at the same time, the received image will at all times be properly placed in its frame of reference Or framed.

It is an object of this invention to provide a synchronizing system in which the synchronizing at one or more tations is controlled by a master source of synchronizing currents.

It is a further object of this invention to provide a synchronizing system in which a plurality of elements at different stations may be caused to operate at the same or synchronous speed, and to take and maintain the same relative position, regardles of a difference in position at the beginning of operation, or at any time therein.

It is still a further object of this invention to provide a synchronizing system in which devices at any station may be set into operation and synchronized with a master source of synchronizing currents in the same relative position in each station without the necessity of manual adjustments.

Still other objects and advantages of my invention will be apparent from the specification.

In accordance with the present invention, I provide apparatus for transmitting periodic impulses 0r signals of some sort at definite time intervals representing definite space positions of the transmitting scanner, and I provide at the receiver apparatus such that if these signals are received at times when the receiving scanner i in an incorrect position, then the receiving scanner is caused to accelerate or retard as the case may be, until the space position of the receiving scanner is correct at the instant of receipt of such signals; when this condition is reached, the accelerating or retarding force is rendered inoperative or ineffective, as long as the desired condition obtains.

For a better understanding of the invention reference may be had to the accompanying drawings, in which:

Figure 1 is a circuit diagram of a transmitter for transmitting signals controlling lightintensity, speed and position a receiving scanner;

Figure 2 a circuit diagram of a receiver adapted for operation on signals received from apparatus such as shown in Figure 1;

Figure 3 is a circuit diagram of a receiver utilizing vacuum tubes for speed and position control;

Figure 4 is a circuit diagram of a slightly modified form of apparatus such as shown in Figure 3; and

Figure 5 is a circuit diagram of receiving apparatus utilizing the phenomenon of resonance for speed and position control.

A typical form of transmitter is disclosed in Figure 1 in which l designates diagrammatically a generator driven by any suitable prime mover, and generating currents of the desired frequency for operating motor II, which in turn operates scanning apparatus at any suitable type, such as herein shown and described, or any other form of scanner known in the art. The apparatus for sending a signal atpredetermined recurrent points, representing definite space positions of the scanner, I term a metronome, and the signal trans mitted thereby I term the metronome signal.

The metronome comprises a suitable source of high frequency currents, such as a vacuum tube oscillator H, from one terminal of which a con-- nection passes to coil I8, thence to the shaft l2,

which drives the scanning apparatus. Mounted on shaft I2 I provide a suitable device for pcriodically closing a circuit through source I! and coil IB. In the form shown, this may comprise conducting disk l3 provided on its periphery with a coating of insulating material except at point l5. Engaging the periphery of disk I3, I may provide a contact finger or brush Hi.

It will be seen that in the operation of this arrangement, coil I8 is momentarily traversed by high frequency oscillations at the instant that conducting point l passes under contact 16, and this may be arranged to take place at the instant that the scanning apparatus, driven from the shaft I2, is operating on the first element of the image.

In the particular arrangement shown, therefore, high or fine frequency oscillations will pass through coil I8 every time the scanning apparatus passes through initial position with reference to the image. It will be understood, however, that the contact may be closed to permit oscillations to pass through coil IS with greater or less frequency, by the interposition of suitable gearing for driving the disk I3, or by other arrangements, as will be understood. A second coil I9 is provided, which may be shunted across the power line connecting the generator l0 and motor II to pass relatively low or coarse frequency oscillations; and a third coil is provided, in which currents are flowing from the output of the photo cell amplifier. The coils l8, l9 and 20, are all coupled to coil 21, which feeds a suitable modulator and oscillator 22, diagrammatically shown, in such manner that the carrier frequency transmitted is modulated by the currents flowing in coils l8, l9 and 20.

The arrangement of said coils, modulator and oscillator, is shown only in diagram, as this a1' rangement per se forms no part of my invention, and is well known in the art. The modulated carrier frequency oscillations are passed through coil 23, and thence to coil 26 inductively coupled thereto, which is connected in circuit with antenna 24, and if desired, a tuning condenser 21 may be associated therewith. It will be understood that all of the modulating currents may be amplified, if desired, to a greater or less extent, and that in case it is desired, one or more of these modulated currents may be impressed as modulations upon separate carrier frequency oscillations which in turn may be used to modulate the carrier frequency of the station. Since the particular apparatus for modulating carrier oscillations, which modulated oscillations are in turn used to modulate another carrier, is well known in the art, his not described in detail.

It will be understood that the signal radiated from the antenna 24 comprises three components: (1) the component indicating the value of light intensity at a, particular time at the transmitter; (2) the currents representing the frequency of the motor generator system Ill and II; and, (3) signals representing the passage of the trans mitting scanning apparatus over a particular point of the frame of reference, and while I have indicated a method and apparatus for transmitting all of these signals of a similar carrier wave, it will be apparent that difficulties of modulation and separation may be avoided if desired, by transmitting each of these signals as modulations of separate carrier waves, each transmitted from a separate antenna or radiating system.

Referring now more particularly to Figure 2, I have shown diagrammatically one form of receiving apparatus, which I term a synchronome, adapted to operate in response to signals transmitted from a system operating as just described. In this arrangement, 30 represents an antenna provided with inductance 3|, shunted if desired, by a tuning condenser 32; the inductance 3| is suitably coupled to a second inductance 33, which feeds the input circuit of a suitable receiver and filter 34, which may comprise as many stages of radio frequency ampliflcation as desired, together with detection and the necessary filtering circuits separating the various signal components from each other and from the received carrier.

The photocell currents are passed to the light control apparatus, as shown diagrammatically by leads designated to light control, and it will be understood that these currents may be a mplified to the extent desired. The currents representing the relatively low or coarse frequency of the motor-generator system Ill and II, may be amplified by suitable amplifier 36, and may be converted, if desired, by means of a converter 31, to currents of the phase desired. In the arrangement shown, I have illustrated the output of converter 31 as being supplied to a suitable three phase motor 38; in this connection, it is desired to point out that preferably motor H and motor 38 should have as near as possible, the same operating characteristics, so that these two motors, under normal conditions, will operate at substantially the same speed or in coarse or approximate synchrony.

To obtain fine synchrony operation of the motor 38 and the motor-generator system 10, H I provide the rotor of motor 38 with a series of coils 44, herein diagrammatically shown for purposes of simplicity, as a single coil, preferably mounted on a pivot at one end so as to be free to align themselves radially under the action of centrifugal force when the motor is operating at substantially synchronous speed. I also provide a series of stationary coils 45, adapted to coact with coils 44 and connected in series therewith through a circuit comprising contact 40 bearing "on slip ring .39 of the shaft 38a of motor 38., and also by means of contact 42 bearing on slip ring 4| insulated from the shaft of motor .38.

The coils 44 and 45 are arranged to be energized by the incoming metronome signals, which may be amplified to the extent desired by the amplifier 35. It will be noted that I provide an insulating segment 43 on the periphery of the disk or slip ring 41, so that the circuit through coils 44 and 45 is periodically interrupted at one point during the revolution of slip ring 41; at all other times, the output circuit of amplifier '35 passes through coil 45 to contact 40, thence to slip ring 39, thence through coil 44 to slip ring M to contact 42, and thence through a suitable tuning condenser 46 to amplifier 35.

The coils 44 should be arranged so. that at speeds substantially less than synchronous speeds, the coils 44 will not be extended radially outward, and Will have very little effect; however, as the motor 33 reaches synchronous speed, these coils will swing into position with their axes extending radially in position to coact with sta-- tionary coil '45; the insulating section 43 is so positioned on the slip ring 4!, that it interrupts the output circuit of amplifier 35 when the position of the receiving scanning apparatus operated by motor 38 corresponds to the position desired; that is to say, in case the transmitter sends out a metronome signal at the instant the scanning apparatus passes across the first element of the image, then the insulating segment 43 will be so positioned with respect to the scanning apparatus driven by motor 38, that insulating segment 43 passes under the contact 42 at the instant that the receiving scanning apparatus driven by the motor 38, passes across the first element of the receiving screen.

If it be assumedthat the motor 38 is operating at the same speed as the motor I I and the instantaneous position of the transmitting and receiving scanning apparatus with respect to the frame of reference, is the same. then the circuit of coils 44 and 45 will be open at the instant the metronome signal is received, and these coil will have no effect. If, on theother hand, as will usually be the case in starting, this condition does not obtain, then the circuit through these coils will be closed, and upon receipt of the metronome signal and during the duration thereof, coils 44 and 45 will operate to attract or repel each other, as the case may be. it being understood that the polarity of all of the coils is so chosen as to obtain maximum action.

For the purpose of discussion, it may be assumed that the coils are so wound, that upon the passage of current therethrough, they are attracted. It will then be apparent that if the motor 38 is operated at less than synchronous speed or is out of proper position with respect to the frame of reference, then every time a metronome signal is received, an impulse will be delivered to the motor 38 tending to speed it up, provided the space relation of the coils 44 and 45 is properly chosen. On the other hand, if the motor 38 is operating at greater than synchronous speed, it is apparent that the position of the coils 44 will be such that it will be retarded by the action of the currents corresponding to the received metronome signal.

In order to prevent a condition of more or less continuous hunting by the motor 33, it may be desirable to arrange the said motor 50 that it will normally operate at a speed relatively a little slower than synchronous speed, so that correcting or accelerating impulses are supplied thereto periodically, so .as to maintain synchronous speed.

It will also be observed that with such an ar- .rangement, regardless of'the. space position of the receiving scanner with respect to the frame of reference, the driving motor cannot operate at synchronous speed until. the correct position with respect to the frame of reference ha been reached, and this makes it possible to provide a single master switch, operable for example by remote control, if desired, which master switch may be arranged to close all the necessary circuits to set the receiving apparatu in operation.

Therefore, it becomes possible to operate a television broadcasting system, requiring no skill on the part of the operator at the various receiving stations, since if the transmitting station is in operation and it is desired to receive from it, the receiving operator need only push a single startstop switch to starting position, whereupon the receiving apparatus will be set into operation, as

; ionic tube 6|.

already described, and will continue to function under the complete control of the transmitting station as long as the master switch is kept closed, no attention being required on the part of the receiving operator.

Referring now more particularly to Figure 3, I have shown diagrammatically another form of synchronome or synchronous receiver for exactly keeping step with the master metronome at the transmitting station. In this arrangement, I have shown the same receiving antenna and frequency filter as indicated in Figure 2, but utilizing thermionic vacuum tubes as controlling devices to differentiate between periodically generated master and local signals.

The received metronome signal, picked up .by the coil 50, is applied to the control electrode 54 of the thermionic tube 5|. This signal is amplified sufficiently to energize the coil 56, controlling the speed of the synchronome motor 58, It will be observed that the tube is provided with the usual cathode 52 and anode 53, which is energized by the battery 51, and the input circuit may include a tuning condenser 55, When the output coil 56 is energized, part of the amplified signal is transferred to the coil 68 to control or block the activity of a similar thermionic tube Bl, having a cathode 62, anode 63 and control electrode 64. The current induced in the coil 68 may be rectified by rectifier 61 of any suitable type. The rectifier when it is energized, passes negative charges, corresponding to the rectified metronome signal, to the control electrode 64 of the therm- This vacuum tube amplifier normally is energized by a local signal; similar to the master metronome signal generated by oscillator 13 and supplied periodically by a contact device H attached to the shaft 10 of the syn-chronome motor. The local or synchronome signal may be produced by a high frequency generator I3, coupled to the synchronome motor 58, when the spring 12 feeds the local signal, which passes through filter 15 to the amplifier GI and through the coils 69 and and a tuning condenser 66 may be provided to strengthen the input signals which pass the filter. Both metronome and synchronome signals should comprise, near synchrony, high frequency oscillations of, preferably, similar periodicity.

When the output coil is energized, a portion of the energy is carried by the associated coil 14 and is rectified by the rectifier 59 so as to pass negative blocking charges to the amplifier 5| from enerator 13. The coils56 and B0 operate to accelerate or retard the synchronome motor 58, except that at speeds much below synchrony, the accelerating coil 58 alone functions. When the motor speeds up sufficiently to cause the generator to pass energy of approximately speed frequency through the filter, then the retarding coil 80 will be able to function in arresting the speed of the synchronome motor.

Which coil operates to control the motor, depends on the advent of distant or local signal. When the metronome energizes the amplifier 5|, it establishes a negative blocking potential on the control electrode 64 of the amplifier GI, and consequently suppresses energy flow in the coil 60. When the synchronome signal energizes the amplifier BI, it establishes a negative blocking potential on the control electrode 54 of the amplifier 5|, and likewise suppresses energy flow in the coil 56.

Accordingly, if the synchronome is running below metronome speed, it is accelerated, and if above it is retarded; in fact, it is maintained at synchrony. The currents in coils 56 and 60 are amplified sufficiently to produce the energy required to control the motor 58.' If the frequency of the currents is low, as for example representing the direct current fluctuations of the tubes BI and BI, then ordinary field coils with magnetic material for reinforcement of the flux may be used. On the other hand, high frequency currents may be applied to these coils with the design of the motor modified to respond to fluctuating currents of higher order.

Moreover, the motor 58 may be driven by local power to approximate synchrony and the load on the coils 56 and 60 may be reduced to values suflicient to exert the required speed variations to maintain synchrony.

Referring now more particularly to Figure 4, in which I indicate again the thermionic controlllngsystem described in Figure 3; I show a polyphase motor synchronome 83 driven synchronously with and by the master metronome l described in Figure 1. The receiver 34 filters and amplifies and supplies to output coil 80 the synchronome signals, described in Figure 3, and to coil 8I the polyphase currents necessary to energize the network system .82 and motor 83 of the synchronome. If the speed developed by the motor 83 is approximately synchronous with the transmitting system I0, II, and the time-phase sufficient to cover a complete scanning element or reference frame as described, then the speed controlling coils 50 and 50 will take care of speed variations within the time and space represented by a single phasing of the motor system. Of course, the speed controlling coil 60 may, at lower speeds than synchrony, have its action cut out by causing, as in Figure 3, the synchronome motor 83 to drive the generator 13 and to suppress its oscillating currents by a filter until the correct frequency is generated and passed to the coil 60, as aforesaid.

On the other hand, the local signal generator I3 may, as shown in Figure 4, be a self-sustaining oscillator whose energy is periodically tapped and transmitted, as indicated, to the retarding coil 60.

The rectifiers 59 or 61, if of the gaseous tube type, may be shunted with suitable impedances 94 and 95, in order to maintain at high frequency rectifications, the tubes and BI sufficiently discharged at the conclusion of the master or local time signals, so as not to block and interfere with the desired operation.

In Figure 5, I show a modified synchronome for attuning by the principle of resonance the local apparatus to the incoming master metronome signals. The receiver 96 delivers the coarse and fine synchronizing signals to coils 94 and 95, respectively, for driving and controlling the synchronome motor 92. By means of shaft I08, the motor drives the wheel I05, which carries peripherally the suspended metallic plate I02 pivoted at I06. This plate is designed near synchronous speed, to engage capacitively corresponding conducting sectors or areas I03 and I04, whose separation apart and distance from the fly plate I02 is adjustable.

The condensive couples I02 and I03, and I02 and I04, when in conjunction near synchronous speed with the master metronome, energize one or other of the two resonant circuits 99 and I00, provided the metronome signal is being sent and received through coil 95, amplifier 91 and the lines IM and I01.

The mode of operation of the resonance synchronizer is as follows: the synchronome 92 ls driven from the receiver 98 through the amplifier 93 at approximate or coarse synchrony, at which, also, the movable condenser plate I02 will fly out sufliciently far, centrifugally, to close, electrostatically, one or other of the resonant circuits containing respectively coils 99 and I00.

For example, if the plates I02 and I03 meet in capacitative conjunction, then high frequency current from amplifie 91 will pass through the momentarily established electric condenser, thus formed, and will energize the coil I00 and amplifier 98; and coil or coils 9| will be strongly energized and may, for example, thus accelerate the speed of the motor 92. Similarly, the coil or coils may retard the motor when the capacitative currents flow through the moving condenser system I02 and I04. Now, when the metronome signal occurs during conjunction of the plates, the synchronome is either expedited or retarded, and at synchrony of the synchronome the fiy plate will be passing just between the plates I03 and I04.

In order to assist rapid acceleration of the synchronome motor 92, the condenser plate I03 taking part in the process may have its functioning area tail off as shown in dotted lines at I09.

In high speed television and synchronization, the wheel I05 should be geared to relatively high speed with the shaft I 08 of the motor 92; the separation between plates I03 and I04 and the Width of the fly plate I02 should be reduced to a minimum. compatible with sharp tuning.

While I have shown and described certain preferred embodiments of my invention, modifications and changes may be made without departing from the spirit and scope of my invention as will be understood by those skilled in the art.

I claim:

1. In a system for synchronizing the operation of a pair of current controlled devices. a source of frequency current to drive the first of said devices, means associated with said first device to generate metronome signals in accordance with the operation of said first device, means to transmit to the second of said devices said metronome signals and signals characteristic of said frequency current, means responsive to the last mentioned signals to cause said sec ond device to operate in at least coarse synchrony with said first device, means associated with said second device to generate synchronome signals in accordance with the operation of said second device, and means responsive to said metronome and synchronome signal to cause said second device to operate in fine synchrony with said first device.

2. In a system for synchronizing the operation of a pair of current controlled devices, a source of relatively low frequency current to drive the first of said devices, means associated with said first device to generate a relatively high frequency current in accordance with the operation of said first device, means to transmit to the second of said devices signals having the low and high frequency characteristics of the aforementioned currents, means responsive to the low frequency characteristic of said signals to cause said second device to operate in at least coarse synchrony with said first, device, means associated with said second device to generate relatively high frequency current in accordance with the operation of said second device, and means responsive to the high frequency currents to cause said second device to operate in fine synchrony with said first device.

3. In a system for synchronizing the operation of a pair of current controlled devices, a source of frequency current to drive the first of said devices, means associated with said first device to generate impulses at a frequency characteristic oil the operation of said first device, means to transmit signals having the frequency characteristics of said current and said impulses, means associated with the econd of said devices to receive and filter said signals, means respon-. sive to the portion of the signals corresponding to said current to cause said second device to operate in at least coarse synchrony with said first device, means associated with said second device to generate impulses at a frequency char? acteristic of the operation of said second device, and means for comparing the impulses gen-. erated by said pair of devices to cause said second device to operate in fine synchrony with said first device.

4. In a system for synchronizing the operation of a pair of current controlled devices, a source of frequency current to drive the first of said devices, means associated with. said. first device to generate metronome impulses in accordance. with the operation of said first device, means to transmit signals to the second of said devices which signals include impulses having the characteristics of said current and the metronome impulses, means associated with said second de; vice to receive and filter said signals, means to amplify the metronome impulses to and cause said second device to operate in at least coarse synchrony with said first device, mean associated with said second device to generate synchronome impulses in accordance with the opera,- tion of said second device, and means responsive to said metronome and synchronome impulses to cause said devices to operate in fine synchrony.

5. In a system for synchronizing the operation of a pair of current controlled devices, a source of frequency current, to drive the first of said devices, means associated with said first device to generate metronome signals in accordance with the operation of said first device, means including modulator and oscillator circuits to broadcast said metronome signals and signals characteristic of said frequency current, means associated with the second of said devices to receive and filter the signals, means responsive tothe signals characteristic of said frequency current to drive said second device in at least coarse synchrony with said first device, means associated with said second device to generate synchronome signals in accordance with the operatio of said second device, and means responsive to said metronome and synchronome signals to cause aid devices to operate in fine synchrony.

6-. In a system for synchronizing the opera tion of a pair of cur-rent controlled devices, asource of frequency current to drive the first of said devices, means associated with said first, device to generate metronome signals in accord-v ance with the operation of said first device, means to transmit said metronome signals and signals characteristic of said frequency current. means associated with the second of said devices to receive and filter said signals, power means for said second device, means including an amplifier responsive to the signal characteristic of said freqeuncycurrent to cause said power means to drive said second device in at least coarse synchronywith said first device, means operated by said power means to generate synchronome signals in accordance with the operation of said second device, and means responsive to said metronome and synchronome signals to cause said power means to operate said second device in fine synchrony with said first device.

7. In a system for synchronizing the operation of a pair of current controlled devices, a source offrequency current to drive the first of said devices, means associated with said first device to generate metronome signals in accordance with themeans to transmit said metronome signals and signals characteristic of said frequency current, means associated with the second of said devices to receive and filter said signals, a threephase motor for said second device, means including an amplifier and a converter responsive to the signals characteristic of said frequency current to cause said motor to drive said second device in at least coarse synchrony with said first device, means operated by said motor to enerate synchronome signals in accordance with the operation of said second device, and means associated with said motor responsive to said.

metronome and synchronome signals to cause said motor to drive said second device in'fine synchrony with said first device.

8. In a system for synchronizing the operation of a pair of current controlled devices, a source of frequency current to drive the first of said devices, means associated with said first de vice to generate metronome signals in accordance with the operation of said first device, means to transmit said metronome signals and signals characteristic, of said frequency current, means associated with the second of said devices to receive and filter said signals, power means for said second device, means including an amplifier responsive, to the signals characteristic of said frequency current to cause said power mean to drive said econd device in at least coarse syn,- chrony with said first, device, means operated by d power m a to ge erate s n h onome s s; nals in accordance with the operation of saidsec- 0nd device, accelerating and retarding circits for said power means, the accelerating circuit being adapted to receive metronome signals and the retarding, circuit being adapted to receive synch o ome si al and said circuits being electrically associated to affect said power means one way or the other whenever the metronome operation of said first device,

and synchronome signals vary from synchronous timed relation.

9. In a system for synchronizing the operation of a pair of current controlled devices, a source of frequency current to drive the first of said devices, means associated with said first device to generate metronome signals in accordance with the operation of said first device, means to transmit said metronome signals and signals characteristic of said frequency current, means associated with the second of said devices to receive and filter said signals, means including an amplifier responsive to the signals characteristic of said frequency current to cause said secand device to operate in at least coarse synchrony with said first device, means associated with said second device to generate synchronome signals in accordance with the operation of said second device, accelerating and retarding circuits for said second device, and means to compare the timing of the metronome and synchronome signals to selectively energize said circuits in accordance with any deviation in the synchronous timing relation of such signals.

10. In a system for synchronizing the operation of a pair of current controlled devices, a source of frequency current to drive the first of said devices, means associated with said first de vice to generate metronome signals in accordance with the operation of said first device, means to transmit said metronome signals and signals characteristic of said frequency current, means associated with the second of said devices to receive and filter said signals, means including an amplifier responsive to the signals characteristic of said frequency current to cause said second device to operate in at least coarse synchrony with said first device, accelerating and retarding resonance circuits for said second device, means to apply said metronome signals on said circuits, and means operated by said second device to establish resonance in one or the other or both of the circuits by closing on one side or the other or at synchrony one or the other or both of the circuits, as the case may be, whereby the operation of said second device is maintained in fine synchrony with said first device.

11. In a system for synchronizing the operation of a pair of current controlled devices, a source offrequency current to drive the first of said devices, means associated with said first device to generate metronome signals in accordance with the operation of said first device, means to transmit said metronome signals and signals characteristic of said frequency current, means associated with the second of said devices to receive and filter said signals, power means for said second device, means responsive to the signals characteristic of said frequency current to cause said power means to start and accelerate said second device to at least coarse synchrony with said first device, means operated by said power means to generate synchronome signals in accordance with the operation of said second device, and means associated with said power means responsive to the establishment of synchrony or near synchrony of the metronome and synchronome signals to cause said second device to operate in fine synchrony with said first device.

12. In a system for synchronizing the operation of a pair of current controlled devices, a source of frequency current to 'drive the first of said devices, means associated with said first device to generate metronome signals in accordance with the operation of said first device, means to .transmit to the second of said devices said metronome signals and signals characteristic of said frequency current, means responsive to the last mentioned signals to cause said second device to start and accelerate to at least coarse synchrony with said first device, means associated with said second device to generate synchronome signals in accordance with the operation of said second device, and means responsive to said metronome and synchronome signals to cause said second device to operate in fine synchrony with said first device.

13. In a system for synchronizing the operation of a pair of current controlled devices, a source of power to drive the first of said devices, means associated with said first device to generate a frequency current in accordance with the operation of said first device, means to transmit to the second of said devices signals having the frequency characteristics of said current, means responsive to the signalsto start and accelerate said second device, means associated with said second device to generate a current, the frequency of which is adapted to be the same as the frequency current generated by said first device when the devices are in synchrony, and means to compare the frequency of the current generated by said second devic with the frequency characteristics of said signals to cause said second device when it reaches synchrony speed to be maintained in synchrony.

14. In a system for synchronizing the operation of a pair of current controlled devices, a source of power to drive the first of said devices, means associated with said first device to generate a frequency current in accordance with the operation of said first device, means to transmit to the second of said devices signals having the frequency characteristics of said current, means responsive to said frequency characteristics of said signals to start and accelerate said second device to the speed of said first device, means associated with said second device to generate a frequency current, means responsive to said last mentioned current to retard said second device, and means to filter said current for passage of frequency currents of the character generated at and beyond synchronous speeds to cause said second device when it reaches synchronous speed to be maintained in synchrony.

15. In a system for synchronizing the operation of a pair of current controlled devices, a source of frequency current to drive the first of said devices, means associated with said first device to generate metronome signals in accordance with the operation of said first device, means to transmit said metronome signals and signals characteristic of said frequency current, means associated with said second device responsive to the signals characteristic of said frequency current to start and accelerate said second device to approximate synchronous speed, accelerating and retarding circuits for said second device, means associated with said second device to generate synchronome signals in accordance with the operation of said second device, and means to compare the timing of said metronome and synchronome signals to determine the energization of said circuits so as to cause said second device when it reaches synchrony speed to be maintained in synchrony.

16. In a system for synchronizing the operation of a pair of current controlled devices, a source of frequency current to drive the first of said devices,

apply said metronom signals on said circuits, and means associated with said second device to establish resonance in one or the other or both of the circuits by closing on one side or the other or at synchrony one or the other or both of the circuits, as the case may be, so as to cause said second device when it reaches synchrony speed to be maintained in synchrony.

ALEXANDER MCLEAN NICOLSON. 

